Abstract Small cell lung cancer (SCLC) is highly aggressive and metastatic malignancy. Unfortunately, no single targeted therapy has shown clinical activity in SCLC and its 5-year survival rate is only 6-8%. Therefore, there is an urgent need to develop innovative strategies against SCLC. In recent years, microRNAs (miRs) have been shown to play significant roles in cancer at the post-translational/transcriptional level by silencing gene expression. Our preliminary data showed reduced expression of miR-1 in SCLC cell lines as well as patient samples. We also observed that miR-1 is inversely associated with CXCR4 in SCLC cell lines and in patient samples. CXCR4/CXCL12-signaling axis has been explored as a major metastatic signaling axis for various cancers including lung cancer. However, not much is known about the role of miR-1 in regulating CXCR4 in SCLC. Our central hypothesis, based on our preliminary data, is that downregulation of miR-1 contributes to SCLC growth and metastasis by upregulating CXCR4. In this application, we propose to develop nanoformulation platform for dual-targeting polymeric CXCR4 antagonist (PCX) nanoparticles (NPs) containing miR-1 mimics for targeting SCLC. We will pursue three specific aims to test our hypothesis. Aim 1 will focus to establish functional miR-1 and CXCR4 axis in SCLC using cell lines and patient samples. These studies will help us to define the novel role of miR-1 downregulation and CXCR4 upregulation for the early detection of SCLC. Additionally, we will perform global transcriptome (miRNA-Seq/RNA-Seq) integrative analysis to explore novel miRs and their targets in SCLC. Aim 2 will be focused on optimization and characterization of PCX-miR-1NPs in SCLC. Since SCLC is highly aggressive and metastatic, we will evaluate whether PCX-miR-1 NPs simultaneously restore miR-1, block the CXCL12/CXCR4 axis, and thereby inhibit metastasis of SCLC in preclinical mouse models. Aim 3 will be designed to analyze therapeutic efficacy of PCX- miR-1NPs in SCLC spontaneous RP (Rbf/f; Tp53f/f; Rosa) mouse model. Upon nasal infection of Ad-cre, RP mice develop tumors that recapitulate human SCLC characteristics. These tumors are highly aggressive and metastatic, and therefore, PCX-miR-1 NPs will serve as ideal nanoformulation-based therapy for the management of SCLC. In addition, cisplatin treatment has been shown to enhance drug resistance through increase CD133+/CXCR4+ cell populations in lung cancer. In this aim, we will also analyze if PCX-miR-1 NPs enhance cisplatin sensitization by reprogramming cancer-associated fibroblasts. Additionally, we will identify novel targets of miR-1 for SCLC using global transcriptome analysis of PCX-miR-1 and cisplatin treated tumor samples. Altogether, the proposed studies will establish the clinical utility of PCX-miR-1 NPs as a novel therapeutic strategy for the treatment of SCLC patients who are difficult to treat due to their advanced disease stage and/or development of drug resistance and recurrence. Nanotechnogy formulation generated in this project will also have broader application in other aggressive and metastatic cancers that have low miR-1 and high CXCR4 expression.